Digital subscriber line (DSL) technologies can provide a large bandwidth for digital communications over existing subscriber lines. Examples of DSL systems include those defined by standards including asymmetric DSL 2 (ADSL2), very-high-speed DSL (VDSL), very-high-speed DSL 2 (VDSL2), G.vector, and G.fast, which is a future standard to be issued by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Study Group 15 (SG15). These broadband access communication technologies may provide data for triple-play services, including television, internet, voice over internet protocol (VOIP) phone.
Subscriber lines in a DSL system typically operate in a noisy environment. Exemplary sources of noise include, but are not limited to, crosstalk, impulse noise, and radio-frequency interference. Further, characteristics of noise(s) may often change over time. Although noise protection mechanisms may be set up during initialization of a subscriber line, the noise protection level can turn out to be inadequate later in showtime, which may result in errors at the end of a receiver and during re-initializations.
In use, a signal-to-noise ratio (SNR) margin may be configured to protect a subscriber line against a sudden increase of noise. Use of SNR margin may be considered a tradeoff between rate-reach performance and immunity to noise. For example, given a certain transmission power on a subscriber line, a higher SNR margin may lead to higher immunity to time-varying noise(s), but also a lower data rate.
On-line reconfiguration (OLR) functions, such as bit-swap, seamless rate adaptation (SRA), and emergency rate reduction, have been defined in current DSL standards to reconfigure data rates on a subscriber line in response to changing line conditions (e.g., an increase or decrease in noise level). Currently-defined OLR functions may all be initiated by a receiver side. Further, a receiver side-initiated OLR procedure may be triggered by SNR measurement, which may sometimes be a relatively slow process. In addition, since a transmitter side needs to respond to a OLR request sent from the receiver side, the receiver side-initiated OLR may require two-way message exchanges before operating with a new configuration. Consequently, a receiver side-initiated OLR may be relatively slow in its response to a noise condition change, which may occur quickly. This mismatch may sometimes result in communication errors from the transmitter to receiver.